This invention relates generally to automatic washing machines and more particularly to automatic clothes washing machines having improved performance during an out-of-balance spin condition.
As it is known in the art, automatic clothes washing machines are cycled through a sequence of operations in the processing of a clothes wash load. For example, these operations may include a presoaking operation, a washing operation, a rinsing operation, and a spin drying operation. The spin drying operation is initiated in order to extract liquid from the clothing. In particular, the clothes are disposed in a perforated spin tub which is rotatably mounted in a stationary drain tub within a washing machine cabinet. During the spin drying operation, the perforated spin tub is rotated at a relatively high rate of speed and the centrifugal force thus produced on the clothing causes liquid to be extracted from the clothing and enter the drain tub through the perforations in the spin tub.
As it is also known in the art, clothing will often be unevenly or non-uniformly distributed during the spin drying operation due to such factors as tangling and irregular masses of clothing. The non-uniform distribution of mass resulting from a concentration of clothing at a given circumferential location during the spin drying operation causes an increase in the centrifugal force at such location, and the spin tub rotates in an out-of-balance condition. A certain amount of load imbalance is a normal occurrence during the spin drying operation. However, when the centrifugal force at the location of the out-of-balance load becomes excessive, high reaction forces are generated and transferred to the floor via the washing machine suspension and the washing machine tends to shake, and in aggravated circumstances physically move or "walk".
One way of minimizing the high reaction forces which tend to cause "walking" is to provide a suspension system which permits a relatively large angular degree of pivoting with minimum resistance. Stated differently, the tendency of the washing machine to "walk" can be reduced by permitting the tub assembly to pivot freely or with a relatively low friction force between the tub assembly and the support structure on which the tub assembly pivots. However, such relatively unrestrained pivoting of the tub assembly necessitates a relatively wide washing machine cabinet in order to prevent the pivoting tub assembly from contacting and perhaps damaging the sides of the cabinet. Thus, while it is desirable to permit relatively unrestrained pivoting with a relatively large angle of pivoting freedom, the friction force should not be so low as to require an undesirably large cabinet. Therefore, the friction force associated with the pivoting of the tub assembly is normally chosen as a trade-off to optimize the out-of-balance performance (i.e. reduce "walking") without sacrificing cabinet size.
As it is also known in the art, washing machines currently utilize a variety of suspension arrangements which provide varying success in reducing the tendency of the washing machines to "walk". For example, conventional base level, fixed pivot suspensions generally include a spherically shaped surface disposed over a complimentary spherical surface provided on a base, or floor level support structure. The drain tub and spin tub mounted therein are elevated above the complimentary shaped spherical surfaces by a vertically oriented drive shaft. Springs are disposed between the bottom of the drain tub and the base level support structure to provide stability to the washing machine.
With this base level, fixed pivot arrangement, the drain tub is free to pivot about the mating complimentary shaped spherical surfaces. Thus, the pivot point is disposed relatively close to the floor and substantially below the tub assembly. Springs with a relatively high rate, or amount of force needed to deflect the spring a unit of distance, are required to maintain the tub assembly in an upright position when the tubs are filled with water and pivoting occurs. Due to the relatively high rate of the springs and the tendency of the tub assembly to vibrate at the critical frequency, the pivoting motion of the tub assembly is damped. Because the motion of the tub assembly is damped, the high centrifugal forces occurring as a result of an out-of-balance load are readily transferred to the floor as high reaction forces and thus initiate "walking".
Another type of suspension arrangement currently used in washing machines is one in which the tub assembly hangs from springs in a pendulum arrangement. This type of suspension generally provides better performance during an out-of-balance load condition than heretofore achieved. However, the improved out-of-balance performance provided by the pendulum type suspension is achieved with substantial penalties. In particular, the washing machine cabinet must be made from more rigid material than was previously necessary due to the tub assembly being supported by the cabinet. Further, there is poor consumer perception associated with this type of washing machine due to the "sinking" of the tub assembly when a wash load is deposited therein.
A third type of washing machine suspension is a midlevel pivot and traverse arrangement. An example of this type of suspension arrangement is found in U.S. Pat. No. 4,174,622 entitled "Automatic Washer Suspension System". The mid-level pivot and traverse suspension includes legs that elevate the support structure to a level approximately mid-way between the washing machine base and the top of the washing machine cabinet. A traversing member is disposed on the support structure and is designed to slide or traverse on such structure. The tub assembly, including the drain tub and the spin tub mounted therein, is disposed over the traversing member. With such arrangement, the pivoting or tilting forces are reduced by the addition of the extra degree of freedom provided by the traversing action. Lower pivoting forces result in lower reaction forces transferred to the floor and thus a reduction in the tendency of the washing machine to "walk".
More specifically, attached to and disposed underneath the drain tub are three inclined pads comprised of a relatively low friction material. When the tub assembly is disposed over the mid-level support structure, the inclined pads attached to the tub assembly mate with complimentary inclined pads disposed on the traversing member. Thus, the tub assembly is free to pivot about the complimentary inclined mating surfaces; and also, the tub assembly can traverse with the traversing member. With this type of washing machine suspension, the spring forces required to hold the tub assembly upright are relatively small since the tub assembly is supported close to the bottom of the drain tub and thus the pivoting moment is smaller than with a base level suspension. Due to the smaller spring forces required and also the horizontal degree of freedom provided by the traversing member, this suspension arrangement is capable of operating with larger out-of-balance loads than the base level, fixed pivot suspension without undesirable "walking" or movement of the washing machine.